Historically, the energy required for the generation of electricity and modern transportation has been largely provided by fossil fuels. Though other energy sources (e.g., wind, solar, hydroelectric, nuclear, etc.) have been developed, used, and are currently available, as a global society, we are still heavily dependent on the combustion of fossil fuels, such as gasoline, diesel fuel, fuel oil, crude oil, coal, and natural gas, to meet our energy and transportation needs. However, with global modernization, the thirst for energy from fossil fuels has grown dramatically, with some estimating that the global energy demand will double within the next several decades.
Increased demand for energy by the global economy has already placed increasing pressure on the cost of fossil fuels and the hydrocarbon products derived therefrom. This trend is particularly troubling when one considers that energy production is just one of multiple critical uses of hydrocarbons. In particular, many industries, including those based on the production or use of composites, plastics, and manufactured chemicals, rely heavily on the availability of hydrocarbons as a feedstock for their processes and products. Therefore, cost-effective alternatives to fossil fuels as an energy and fuel source would not only help provide for the world's increasing demand for energy, but could also help mitigate the upward cost pressure recently experienced with products produced from fossil fuels.
Energy derived from biomass presents a means of both potentially reducing greenhouse gas emissions and reducing the need for a fossil fuel-based infrastructure, and bioenergy is generally considered to be an important asset in our repertoire of renewable energy solutions. In biological systems, the utilization of energy is accomplished by a cascade of biochemical reactions mediated by tightly regulated metabolic networks.
Microbes such as microalgae show promise as a renewable feedstock for the production of biofuels ranging from ethanol to biodiesel. Algae are a diverse group of aquatic, photosynthetic organisms generally categorized as either macroalgae (i.e., seaweed) or microalgae, which are typically unicellular. Although the field of algal biofuels remains in its infancy, microalgae have great potential to serve as a resource for clean, sustainable fuel production. Algae are effective photosynthetic organisms for generating chemical energy from sunlight, and it is believed that a large percentage of today's fossil fuels, particularly petroleum, originated as prehistoric algal blooms. As single-celled organisms, microalgae are capable of producing a large portion of their biomass as small molecule biofuel precursors since they lack the macromolecular structural and vascular components needed to support and nourish terrestrial plants. As such, algae provide one of the most direct routes for conversion of carbon and other organic substrates to biofuel. Moreover, the large surface area to volume ratio of these aquatic microorganisms is advantageous for absorption of nutrients, which is reflected in the rapid growth rates observed in many species.
Unlike terrestrial bioenergy crops, microalgae do not require fertile land or extensive irrigation and can be harvested continuously. Several species of microalgae do not even require freshwater and may grow in brackish, sea, and even hypersaline water. Additionally, since microalgae consume carbon dioxide (CO2) through the process of photosynthesis, large-scale cultivation may even be used to remediate the CO2 emissions from fossil fuel combustion. Algae biomass also possesses marketable, secondary co-products such as antioxidant pigments, edible proteins, and nutraceutical oils that other alternative fuel crops lack. Nevertheless, hurdles to large-scale commercialization of algal biofuels remain. Among such challenges are: (1) the need to increase algal oil productivity; and (2) the need to improve processing techniques required to access the oil produced by algae.